Gravimetry can be used to identify hydrocarbon reservoirs within underground formations and to characterize those hydrocarbon reservoirs on a large-scale. In particular, a device called a “gravimeter” can be used to determine a measure of gravitational acceleration at a particular location adjacent to an underground formation. This measure of gravitational acceleration can be used to determine characteristics of the underground formation, such as the bulk density or specific gravity of the underground formation.
One example of a conventional gravimeter is a Lacoste-Romberg gravimeter. A Lacoste-Romberg gravimeter uses a zero-length spring to monitor gravitational force that is applied to a small proof mass. Conventional gravimeters also use other technologies. For example, other conventional gravimeters use the time of flight of a free-falling object or the oscillation time of a pendulum to determine gravitational acceleration. In yet other examples, gravimeters use cold atomic fountains, current-carrying vibrating strings, or torsion balances to determine the force of gravity.
Such conventional gravimeters and other available gravimeters are difficult to adapt to rugged borehole environments. High temperatures and dynamic temperatures are common in borehole environments (e.g., 175° C. and above). Furthermore, tools that enter borehole environments are often subject to shock and vibrations. These problems are compounded because the gravitational force is an extremely weak force. Such conditions make it challenging to achieve the sensitivities for an accurate gravimetric measurement.